The invention relates to a leaf-spring rear axle vehicle suspension, particularly for light commercial vehicles which have a rigid rear axle body provided with longitudinally extending leaf springs with eyelets formed at their front ends by way of which they are mounted to a vehicle body via elastic sleeves and which are supported at their rear ends by a support structure permitting longitudinal movement of the rear ends of the leaf springs.
Rear axle suspension of the above type are known, for example, from the book by Jxc3x6rnsen Reimpell, Fahrwerkstechnik 1, Vogel-Verlag, Wxc3xcrzburg, 1970, page 100. With respect to an understeer behavior when negotiating curves, the rear axle body is guided by longitudinally extending leaf springs which are arranged at opposite ends of the axle body and hinged to the vehicle body and which extend from a rear hinge location forwardly in a downwardly inclined manner. In this way, the different spring travelsxe2x80x94spring compression at the outer axle (with respect to the curve) and spring release at the inner axle can be converted to longitudinal movements of the axle body such that the axle body is moved forwardly at curve-outer axle end and rearwardly at the inner axle end. In this way, a position of the axle is obtained in which it is inclined with respect to the vehicle travel direction so that the rear axle steers inwardly into the curve, which results in an understeering vehicle behavior. Such an operation depends on the movements of the vehicle body which is why such a steering behavior is called roll steering which, because of its dependency on the vehicle body movements is relatively slow and which, particularly with other non-symmetric spring movements provides for undesirable steering effects. Furthermore, the design conditions must permit such a mounting of the leaf springs at different front and rear height levels or the vehicle design must be adapted and this may affect other vehicle design features.
The elastic bearings to be disposed in the eyelet support structures of the longitudinal leaf springs comprise generally elastic bearing sleeves which include inner and outer sleeve members and which are inserted, or pressed, into the spring eyelet. With regard to an acoustic uncoupling, the sleeves are, with an exact axle guide structure, generally radially relatively soft and axially, that is, in the transverse vehicle direction, relatively stiff. (DE 40 42 201 C1).
For achieving side force-dependent understeer effects, it is known, for example, from DE OS 178 0209, to mount or anchor the wheel support members with regard to the vehicle body by way of a common axle carrier which is often also called an equalizing truck and to attach the wheel support member to the axle carrier by way of elastic elements. These elastic elements are so formed and/or arranged that, with respect to side forces, tilt or roll movements occur about a pivot pole which is disposed behind the center of the axle. With regard to comfort, but also with regard to an improved force transfer to the vehicle body and/or a better positioning of the attachment of the wheel guide members to the vehicle body such solutions are often found to be expedient but they require additional expenses.
It is therefore the object of the present invention to provide a leaf-spring rear axle suspension for vehicles, particularly for light commercial vehicles, with which the advantages of present designs particularly their economical advantages with regard to a side force-depending understeer behavior are maintained but to improve the operating behavior and handling of such vehicles.
In a leaf spring suspension for a rear vehicle axle including a rigid axle body, wherein the suspension comprises leaf springs extending in the longitudinal direction of the vehicle at opposite sides of the vehicle and the leaf springs have front and rear end supports by way of which they are mounted to the vehicle body, the rear supports for supporting the springs on the vehicle body in a longitudinally displaceable manner are stiff in a transverse direction and the front supports are resilient in a transverse direction such that, when the vehicle is subjected to side forces, a pivot pole is established for the rear axle which is disposed behind the center of the rear axle.
With the sidewardly soft support for the front end of the leaf springs and a stiff sideward support of the rear support of the leaf spring a roll center is formed when side forces are effective on the vehicle body, that is a pivot pole is established by the wheel suspension, which pivot pole is behind the center of the axle. In this way, the longitudinal leaf springs can pivot slightly about the rear supports of the vehicle body on the springs, like with a parallel arm suspension, so that, depending on the respective curve direction that is depending on the side forces resulting therefrom, the axle body is slightly inclined with respect to the longitudinal vehicle direction so as to provide for understeering of the vehicle when negotiating a curve.
The solution according to the invention does not require any changes of the proven design concept of leaf spring rear axle suspensions for driven or non-driven axles and may be particularly advantageously utilized in connection with light commercial vehicles. The invention can be expediently realized in connection with conventional leaf spring designs without the need for any design changes and without the need for changing the leaf springs.
With respect to the desired comfort-improving suspension and the desired understeer characteristics, a design is particularly expedient, wherein, with a spring eyelet of oval shape, whose greater axis extends in the longitudinal direction of the spring, a structure with an elastic movability normal to a line inclined to a transverse vehicle direction and extending essentially through the pivot pole relative to the respective support console and which provides for an elasticity in a vertical direction, is provided. The elastic sleeves of the bearings have essentially the same thickness so that also the size requirements are the same as in comparable conventional designs. To this end, it is expedient, if the elastic sleeves are slightly oval corresponding to the spring eyelet, wherein the axis of the sleeve is inclined with respect to the axis of the spring eyelet. The inner sleeve area is formed by a bearing core in the form of a cylinder which is inclined with respect to the sleeve, notwithstanding the sleeve opening being parallel to the axis of the spring eyelet, which sleeve opening forms the reception bore for a mounting bolt. The reception bore is disposed in the area of front projections, which extend beyond the side stops of the bearing. The projections form the side support with respect to the support console, so that proper assembly is ensured by fitting projections and recesses during assembly.
The outer sleeve of the bearing is, corresponding to the contour of the eye of the spring, an annular body of oval cross-section with annular walls, which extend parallel to the bearing axis, which coincides with the eyelet axis. As a result, the inner sleeve, whose axis extends at an angle to the eye and bearing axis, forms in a transverse cross-sectional view, wedge shaped and circumferentially sickel-shaped spaces between the outer and the inner sleeves, which spaces at the opposite sides of the inner sleeve are oriented in opposite directions and are filled with inserts. The inserts are guide means and are therefore expediently of a hard material. They may be formed by in situ injection molded structures attached to the outer sleeve. The arrangement provides for understeer effects, which are obtained thereby with little expense. The arrangement can be provided inexpensively by only minor modifications of the conventional bearing structures in the eyelets of the leaf springs. The springs themselves are not modified and may be used in connection with other bearing designs for similar vehicles.
Comparable effects can be reached in accordance with the invention with the bearings for the front supports of the two longitudinal leaf springs of a suspension mounted in the eyelets of the springs in the same manner, if the bearings of the front supports of the two longitudinal leaf springs are, particulary with the axes of the bearing sleeves aligned, supported with a certain longitudinal resiliency, in addition to the transverse resiliency, which longitudinal resiliency however is substantially less than the transverse resiliency the resiliency in the transverse direction being 2 to 3 times the resiliency in the longitudinal direction of the vehicle. The soft support in transverse direction provides over a small range around the neutral design position a support without distance-dependent hardening, but then becomes progressively stiffer. This permits in connection with the, in transverse direction, rigid rear supports a transverse displacement of the rear axle suspension in the area of the front supports of the leaf springs which causes the pivot pole of the suspension to be placed behind the center of the axle and results in comfortable longitudinal spring characteristics. Longitudinal vibrations can be prevented in accordance with a particular embodiment of the invention by dampening the rear support in respect to longitudinal movements. This can be achieved in a simple manner by a dampening slide bearing mount of the rear spring support, for example by way of compensation shackles, which are supported on the body in a dry sliding manner.
Such a construction of the rear axle suspension is possible in connection with oval as well as round bearings. With the appropriate hollow spaces in the elastic bearing sleeves, the desired rigidity can be obtained in a simple manner without other design features.
Various embodiments and features of the invention will be described below in greater detail on the basis of the accompanying drawings.